Definition
Defining attribute
A defining attribute is a feature a shape must have to belong to a named class.
Continue from this idea into connected AXIO math.
Boundary check: Size and orientation change; three straight sides remain required.
What it means
It works like an entry rule for a shape group. If the rule is missing, the shape does not belong. Every triangle must be closed and have three straight sides, whatever its colour, size, or tilt.
Remember it
Defining means required: change it, and the shape may leave the group.
Example
Mia draws a closed figure with three straight sides. Those attributes make it a triangle, even though one side points downward.
Watch for
A feature can be defining for one class but not another: equal side lengths define an equilateral triangle, but not every triangle.
Common mix-up
A feature that many examples happen to share is not defining unless every member of the named class must have it.
Exact meaning
A defining attribute of a shape class is a property that every member of that class must have.